1. Field
Provided is a liquid crystal display device including a white light emitting diode.
2. Description of the Related Art
A white light emitting diode (“LED”) using a semiconductor is in the spotlight as one of the next generation light emitting devices that is capable of replacing existing light emitting devices, due to its long life-span, capability of being down-sized, low power consumption, and environmentally friendly characteristic of being mercury free. The white light emitting diode is also used for an instrument panel of automobiles, a backlight of liquid crystal displays (“LCDs”), and the like.
Particularly, for use as a backlight of a liquid crystal display, a method of using a tri-color (e.g., red, green, and blue) light emitting diode having excellent efficiency and color purity has been suggested. However using the tri-color (e.g., red, green, and blue) light emitting diode has a drawback of low price competitiveness due to its high manufacturing cost and complicated operation circuit. Thus, there is a demand for the development of a one-chip solution that can reduce manufacture cost and simplify the construction of a device, while maintaining efficiency and color purity performance similar to the existing method.
As one of the one-chip solutions, a white LED that combines an indium gallium nitride (InGaN) series blue light emitting diode having a wavelength of about 450 nanometer (nm) with a cerium-doped yttrium aluminum garnet (“YAG:Ce”) phosphor has been developed. The operation principle of the light emitting diode is that a portion of blue light generated in the blue light emitting diode excites the YAG:Ce phosphor to generate a yellow-green color, and the blue and the yellow-green colors are composed to emit white light.
However, since the white LED light combining the blue light emitting diode with the YAG:Ce phosphor includes only a portion of the spectrum of the visible ray region, the white LED light has a low color rendering index. Consequently, when passing through a red, green and blue color filter, many portions of the white LED light fail to pass through the color filter thus causing efficiency loss. Thereby, the white LED light passing through the red, green and blue color filter has low color purity, and thus is not suitable for a display device requiring high definition such as a television (“TV”).
Recently, a method of manufacturing a white light emitting diode using an ultraviolet (“UV”) light emitting diode, that is expected to have high energy efficiency as an excitation source rather than a blue light emitting diode, and using a blue, green, and red light emitting source, has been researched. However, it is currently required to develop a red light emitting source having high efficiency compared to blue and green.
As another method, a method of coating green and red inorganic phosphors on a blue light emitting diode has been attempted. However, a suitable material that is capable of exciting an inorganic phosphor that is excited by relatively high energy to a blue wavelength of the visible light region, has not yet been developed, and a thus-far developed green phosphor has low stability and color purity. Further, a problem of low efficiency of a red phosphor has not yet been settled, and thus the method of coating green and red inorganic phosphors on a blue light emitting diode has a limitation in that color purity and light efficiency required in a light emitting diode for a backlight unit cannot be secured.